In recent years, portable electronic equipment, such as Personal Digital Assistance (PDA) and mobile phones, has been rapidly expanding its market, and getting smaller in size. At the same time, a magnetic disk drive unit, which has become commonly used as a handy storage device, has been required to have smaller and thinner body with increased toughness against shocks. Responding to the need for the unit with high-impact-resistance, various attempts have been made to offer improvements in a head supporting mechanism of a magnetic disk drive unit.
For example, employing a L/UL mechanism for a disk drive unit has been recognized as an effective way for providing an impact-resistant disk drive unit. Magnetic disk drive unit 129, as shown in FIG. 7, has a head supporting device equipped with L/UL mechanism. Support arm 102 has guide 102a at its tip; and has magnetic head-mounted slider 101 in the proximity of the tip. Driven by spindle motor 105, magnetic recording medium 112 starts rotating. During the rotating, slider 101 mounting a magnetic head (not shown) thereon levitates at a position over medium 112 for data writing or reading. This state is the loading mode in the U/L mechanism.
On the other hand, when medium 112 stops rotating, support arm 102 rotates on rotation axis 103c and moves toward the outside of medium 112. The movement of arm support 102 is controlled by voice coil motor (hereinafter referred to as VCM) 124, which operates on interaction between voice coil 116 disposed at support arm 102 and, magnet 120 and yokes (not shown) that sandwich voice coil 116 via a clearance. Ramp 118 having tapered portion 118a is formed at the outside of medium 112. Driven by VCM 124, support arm 102 withdraws from the surface to take guide 102a onto ramp 118. This “withdrawal” allows slider 101 to keep off medium 112—the magnetic head is in the unloading mode. The head supporting device shown in FIG. 7 employs locking mechanism 130 using a piece of iron and a magnet for supporting the arm.
In magnetic disk drive unit 129 having the head supporting device as described above, the magnetic head is kept away from medium 112 during the unloading mode. The structure prevents the head and a medium against shocks from outside. Compared to other systems, the L/UL system has decreased the chance of mechanically or magnetically damaging medium 112 by collision with the head.
However, it is also true that the L/UL mechanism-employed disk drive unit has a problem to be tackled: a rather large sliding load. When guide 102a runs onto tapered portion 118a of ramp 118, the load on the arm due to the “landing” surpasses the half of torque required for the VCM. In a multi-disk structure having a number of heads, the built-up load has been a serious problem. Besides, downsized magnetic disk imposes limitations on the VCM components including the coil, the yoke, and the magnet: the number of turns of the coil reduces due to the thinned coil; the magnetic circuit formed of thinned VCM components cannot capture sufficient fluxes. Such inconvenience inevitably reduces the torque of the VCM.
It has therefore been a significant challenge for manufacturers to reduce the load on the VCM. Addressing to the inconvenience, there have been many suggestions to decrease the load developed in the unloading motion of the arm. The followings are the examples: i) in Japanese Patent Publication No. JP7334955, a ball bearing is disposed on the surface of the guide where the tapered portion comes in contact so as to decrease the coefficient of friction of the tapered portion and the guide of the arm; ii) in Japanese Patent Publication No. JP1196699, a piece of iron and a locking magnet are added to a coil-holding member of the VCM. Magnetic interaction between the iron piece and the locking magnet provides the arm with a smooth turn, thereby reducing the load on the VCM. At the same time, the suggestion includes a guiding-and-locking system for a rotary actuator to protect components of the unit from an impact generated in the process of the unloading motion.
Still, the two suggestions shown above have problems to be solved: as for the former suggestion described in i), it needs an extremely high technique to dispose the ball bearing in the tiny space of the guide at the tip of the support arm in such downsized disk drive unit, thereby automatically decreasing productivity. Besides, mounting an additional part on the tip of the arm lowers the resonance frequency of the arm. When the arm is moved at a high speed, the lowered resonance frequency generates undesired various vibration modes, which requires the disk drive unit a time to get settled. The fact has been an obstacle to rapid data access. As for the latter one described in ii), disposing an extra locking system not only introduces a complication on downsizing the magnetic disk drive unit but also increases the cost.
Prior-art head supporting devices including the two examples above have similar structures: the support arm rotating on a spindle moves the slider substantially parallel to the surface of the recording medium; a resilient member including a spring is disposed between the spindle and the arm, or between the arm and a head-supporting member to apply force to the slider; the force works on the slider to levitate it with a fixed interval from the surface of the medium. In the prior-art, it has never been discussed the possibility that a vertical movement of the arm with respect to the medium surface can reduce the load on the VCM. Manufacturers have not reached subtle solutions to the reduction of the load on the VCM.